1. Field of the Invention
This invention relates generally to methods and systems for ionization of a sample. More specifically, this invention comprises methods and systems for generating reagent ions to interact with a sample to produce ions from the sample.
2. Description of the Related Art
There is a present and growing need to detect a wide variety of chemicals as solids, liquids and vapor, resident in air or solutions, or on surfaces. The potential analytes from these chemicals can include, for example, chemical warfare agents, pesticides, pollutants, drugs, explosives, and other chemicals under process control. Depending upon the chemicals, their physical properties, and the means of their dispersal, these chemicals can be present in air as vapor, aerosol or particulate matter; in water or solvents as solutions or emulsions; or on surfaces such as concrete, asphalt, paper or textiles. A common feature underlying most of these organic chemicals is that they can be ionized. Once a chemical is ionized, it can be detected by many different sensors.
Conventional sensors can exploit molecular charge, size, shape, or other specific characteristics to distinguish one ionized chemical from others and provide identification. A device, particularly if it were handheld, that could ionize chemicals as vapors, liquids or solids whether they be in air or other gases, in solutions, or on surfaces would, therefore, be desirable to extend the capabilities of many ion-dependent sensors. It would also be desirable if, as a consequence of ionization, the device did not fragment the chemical into an abundance of different ions, which can make detection and identification more difficult.
A very wide range of chemicals can be ionized using a two step process. First, reactant ions such as O2− or H+(H2O)n are created. Upon contacting these ions, many chemicals are subsequently ionized, and these ions can then be detected. However, although conventional devices and methods attempt to accomplish positive ion chemical ionization at atmospheric pressure, there is a need for simple and reproducible means to perform atmospheric pressure chemical ionization using negative ions. Radioactive elements, such as 63Ni, can be used to ionize chemicals, particularly in handheld detectors. However, the owner or users of the device are burdened with logistical matters, such as licensing, reporting, and disposal requirements, involving the use of radioactive material. Non-radioactive ionization sources, such as gas discharge devices, eliminate such logistical concerns, but pose a different set of challenges. For example, power consumption and size may not be consistent with intended usage. It can be very difficult to control the discharge so that over long periods of usage only the desired ions are produced and the undesirable ions are not produced. Degradation of performance must be avoided from parts that wear out as a consequence of the discharge. Furthermore, there are many types of gas discharge devices, each having its own power and configuration requirements that can limit utility in a desired application. Finally, the need for helium or other bottled gas may render a particular device impractical for handheld, portable applications.